Vasodilators and more recently calcium flux antagonists are being widely used in the treatment of patients with coronary artery disease. The effects of these agents on the transmural distribution of coronary blood flow and myocardial contraction at various degrees of coronary stenosis are largely unknown. Therefore, we propose a systematic study of the effects of nitroglycerin, nitroprusside, nifedipine and verapamil on regional myocardial blood flow and contraction. This study will be carried out in open chest dogs subjected to varying levels of partial coronary occlusion. Regional myocardial blood flow will be measured with tracer microspheres and myocardial contraction with ultrasonic segment length gauges implanted in the endocardium and epicardium. The degree of stenosis will be monitored by perfusion pressure and by an electromagnetic flow probe. Segment motion and hemodynamics will be recorded and microspheres given during a control period, after occlusion and after a drug intervention. The drugs in the initial studies will be given intracoronary to clarify their direct effects and in subsequent studies intravenously to evaluate modifications resulting from systemic vascular effects. These studies should help elucidate the conditions in which these drugs are most useful and situations in which they may be deleterious.